ERCOT STEADY STATE WORKING GROUP
PROCEDURE MANUAL
February 11, 2010
ERCOT STEADY-STATE WORKING GROUP’S SCOPE
The ERCOT Steady-State Working Group (SSWG) operates under the direction of the Reliability and Operations Subcommittee (ROS). The SSWG’s main objectives are to produce seasonal and future load-flow base cases, coordinate tie-line data, update the Most Limiting Series Element Database, maintain the ERCOT Data Dictionary, update the SSWG Procedural Manual, prepare data for and review seasonal transmission loss factor calculation, and provide requested transmission system data and power-flow support documents to market participants. The SSWG usually meets in June and November to accomplish these tasks, and at other times during the year as needed to resolve any impending load-flow modeling issues or to provide technical support to the ROS. Some of the above responsibilities are further described as follows:
· Develop and maintain load-flow base cases for the spring, summer, fall, and winter seasons of the upcoming year. The cases, collectively known as Data Set A, are produced by the SSWG by approximately July 1st on an annual basis. These seasonal cases consist of one on peak and one off-peak case for each of the four seasons.
· Develop and maintain load-flow base cases for the five future years following the upcoming year. The cases, collectively known as Data Set B, are produced by the SSWG by approximately November 15th on an annual basis. These future cases consist of five summer on-peak cases, and one minimum case. Data Set B will contain economically dispatched generation (ECO)
· Maintain and update the ERCOT Data Dictionary to reflect new bus information and SCADA names. This task is performed during the Data Set B work.
· Maintain and update the SSWG Procedural Manual to reflect current planning practices and the latest load-flow base case modeling methodologies.
· Prepare data for and review seasonal transmission loss factor calculation on an annual basis. This task is to be done by approximately January 1st.
· Each TDSP shall maintain an MLSE database and will make the data available to ERCOT upon request.
· Assist in development of ERCOT processes for compliance with NERC Reliability Standards for both entity and region-wide requirements.
· Coordinate tie-line data submission to ERCOT with neighboring companies.
· Provide Transmission Project Information Tracking (TPIT) report to ERCOT quarterly.
· Maintain and update the contingencies files.
· Address issues identified by ERCOT Reliability Assessment
· Perform studies as directed by the ROS.
Table of Contents
SECTION 1.0 – Data Requirements 4
1.1 General 4
1.2 Bus Data 5
1.3 Load Data 6
1.4 Generator Data 7
1.5 Line Data 11
1.6 Transformer Data 19
1.7 Static Reactive Devices 22
1.8 Dynamic Control Devices 24
1.9 HVDC Devices 27
SECTION 2.0 – Load-flow Procedures and Schedules 30
2.1 Data Set A Considerations 30
2.2 Data Set B Considerations 32
2.3 Error Screening and Case Updates 34
SECTION 3.0 – Other SSWG Activities 37
3.1 Transmission Loss Factor Calculation … 37
3.2 Contingency Database………………………………...... 38
APPENDICES 41
A Owner ID, TSP, Bus/Zone Range and Tables 41
B Glossary of Terms 53
C TSP Impedance and Line Ratings Assumptions 54
D MLSE 68
E TPIT 69
F Treatment of Mothballed Units in Planning 70
G Load Forecasting Methodology 72
H Transmission Element Naming Convention 80
I Method for Calculating Wind Generation Levels in SSWG Cases………….81
J Mexico’s Transmission System in ERCOT SSWG Cases.…………….……..82
SECTION 1.0 – Data Requirements
1.1 GENERAL
The principal function of the SSWG is to provide analytical support of the ERCOT electrical transmission network from a steady state perspective. To accomplish this, the Working Group performs three principal charges: load-flow, voltage control and reactive planning, and transmission loss factor calculation tasks.
1.1.1 Coordination with ERCOT
Load-flow base cases provide detailed representation of the electric system for planning and evaluating the current and future high voltage electrical system and the effects of new loads, generating stations, interconnections, and transmission lines.
1.1.2 Model
The model represents the high voltage system, branches, buses, bus components, impedances, loads, multi-section lines, ownership, switched shunts, transformers, generators, DC lines and zones. The network model submitted by the TSP shall be in a format compatible with the latest approved PSS/E and rawd ASCII data format based on a 100 MVA base. The model should reflect expected system operation.
1.1.3 Data
The SSWG will use loads based upon the load data in the ERCOT Annual Load Data Request (ALDR) to build two sets of cases, Data Set A and Data Set B (see Sections 2.1 and 2.2). Reference appendix G.
Data Set A consists of seasonal cases for the following year. The SSWG must finalize Data Set A by early July to meet ERCOT schedule to perform the commercially significant constraint studies. Data Set B, which is finalized in mid-October, is used for planning purposes and consists of the following:
· Future summer peak planning cases
· A future minimum load planning case
· ERCOT Data Dictionary
· Updated Contingency List
1.1.4 Load-flow Case Uses
The cases being created each year are listed in Sections 2.1 and 2.2. ERCOT SYSTEM PLANNING (ESP) and Transmission Service Providers (TSPs) test the interconnected systems modeled in the cases against the ERCOT Planning Criteria to assess system reliability in the coming year and into the future. ROS Working Groups and ERCOT System Operations use SSWG cases as the basis for other types of calculations and studies:
· Internal planning studies and generation interconnection studies
· Voltage control and reactive planning studies
· Dynamics Working Group stability studies
· ERCOT transmission loss factor calculation
· Basis for ERCOT operating cases and FERC 715 filing
· Commercially significant constraints studies
1.2 BUS DATA
1.2.1 Areas defined by TSP
Each TSP is assigned a unique area name and number denoted in the TSP Bus/Zone Range Table in Appendix A.
1.2.2 Bus Data Records
All in-service transmission (60kV and above) and generator terminals shall be modeled in load-flow cases. Each bus record has a bus number, name, base kV, bus type code, real component of shunt admittance, reactive component of shunt admittance, area number, zone number, per-unit bus nominal voltage magnitude, bus voltage phase angle, and owner id. Fixed reactive resources shall be modeled as a fixed component in the switchable shunt data record and not be part of the bus record.
1.2.3 Bus Ranges
Presently, ERCOT is modeled within a 100,000-bus range. The Chairman of the SSWG allocates bus ranges, new or amended, with confirmation from the SSWG members. Bus ranges are based on high-side bus ownership. (Refer to TSP Bus/Zone Range Table in Appendix A)
Bus numbers from within the TSP’s designated bus range are assigned by the TSP and are to remain in the assigned ranges until the equipment or condition that it represents in the ERCOT load-flow cases changes or is removed.
1.2.4 Zone Ranges
Presently the Chairman of the SSWG allocates zone ranges, new or amended, with confirmation from SSWG members. Each TSP represents their network in the ERCOT load-flow cases using allocated zone ranges. Zone numbers that have been assigned by the TSP, within the TSP’s designated zone range, may be changed by the TSP as needed to represent their network in the ERCOT load-flow cases. Every zone number assigned must be from the TSP’s designated zone range. Zone identifiers are specified in zone data records. Each data record has a zone number and a zone name identifier. (Refer to TSP Bus/Zone Range Table in Appendix A).
1.2.5 Owner IDs
All TSPs may provide owner IDs for buses. This data is maintained in the Owner ID, TSP Bus/Zone Range Table shown in Appendix A. The generation owner ID’s are not in the cases due to the difficulty in tracking the continuously changing ownership.
1.2.6 Bus Name
Electrical Bus names shall not identify the customers or owners of loads or generation at new buses unless requested by customers. The twelve characters Electrical Bus Name representing individual transmission element in the planning model shall be unique and follow certain technical criteria as stated in the ERCOT Nodal Protocol Section 3.10. (Refer to Transmission Element Naming Convention in Appendix H)
1.3 LOAD DATA
Each bus modeling a load must contain at least one load data record. Each load data record contains a bus number, load identifier, load status, area, zone, real and reactive power components of constant MVA load, real and reactive power components of constant current load, and real and reactive power components of constant admittance load. All loads (MW and MVAR) should be modeled on the high side of transformers serving load at less than 60 kV.
Guidelines:
1.3.1 The bus number in the load data record must be a bus that exists in the base case. As of 2001 owner IDs shall not be associated with any entity in cases. The load identifier is a two-character alphanumeric identifier used to differentiate between loads at a bus. All self-serve loads must be identified by “SS”. If there are multiple self-serve loads at the same bus, then the self-serve loads will be identified by S1, S2, S3, etc. See Section 1.4.1. Partial self-serve load should be modeled as a multiple load with “SS” identifying the self-serve portion. Distributed generation must be identified by “DG” and modeled as negative load.
1.3.2 The load data record zone number must be in the zone range of the TSP serving the load. It does not have to be the same zone that the bus is assigned to.
1.3.3 Generator auxiliary load should not be modeled at generating station buses. Refer to section 1.4.1.
1.3.4 In conformance to NERC Planning Requirements and the ERCOT Operating Guides Section 5.1.2, which states “ Each ERCOT DSP directly interconnected with the transmission system (or its agent so designated to ERCOT) shall provide annual load forecasts to ERCOT as outlined in the ERCOT Annual Load Data Request (ALDR) Procedures. For each substation not owned by either a TSP or a DSP, the owner shall provide a substation load forecast to the directly connected TDSP sufficient to allow it to adequately include that substation in its ALDR response.” Entities not having representation on SSWG shall submit the data to ERCOT or if the directly connected TDSP has agreed to be the agent on SSWG for that entity, to that TSP. If load data is not timely submitted on the schedule and in the format defined by the TSP, then ERCOT shall calculate loads based on historical data and insert these loads into the load flow cases during DataSetA and DataSetB annual updates.
1.3.5 Multiple loads from different TSPs at a bus may be used. At this time, each TSP can define a load however it wishes with a load ID of its choice though careful coordination is required between TSP representatives to ensure that the loads at the bus get modeled correctly.
1.4 GENERATOR DATA
1.4.1 Acquisition of Generator Data
Only net real and reactive generator outputs and ratings should be modeled in load-flow cases. Net generation is equal to the gross generation minus station auxiliaries and other internal power requirements. All non-self-serve generation connected at 60kV and above with at least 10 MW aggregated at the point of interconnect must be explicitly modeled. A generator explicitly modeled must include generator step-up transformer and actual no-load tap position. Generation of less than 10 MW is still required to be modeled, but not explicitly.
Unit reactive limits (leading and lagging) for existing units should be obtained from the most recent generator reactive unit test data provided by ERCOT. For units that have not been tested, limits will be obtained from the generator owner. Unit reactive limits (leading and lagging) are tested at least once every two years (ERCOT Protocols, Section 6.10.3.5 and ERCOT Operating Guides, Section 6.2.3). If the test does not meet these requirements, reference the ERCOT Operating Guides for further explanation or actions. Note that the CURL MVAr values are gross values at the generator terminals. Limited ERCOT RARF data shall be made available to SSWG upon request.
Generator reactive limits should be modeled by one value for Qmax and one value for Qmin as described below:
Qmax
Qmax is the maximum net lagging MVAr observed at the low side of the generator step up transformer when the unit is operating at its maximum net dependable MW capability. Qmax is calculated from the lagging CURL value by subtracting any auxiliary MVAr loads and any Load Host MVAr (Self Serve) load served from the low side of the generator step up transformer.
Example:
Lagging CURL value is 85 MVAr
Lagging test value is 80 MVAr
Auxiliary Load is 5 MVAr [1]
Qmax is 85 – 5 = 80 MVAr (Use the CURL value here if the test value is equal to or greater than 90% of the CURL. Use the test value here if the test value is less than 90% of the CURL.)
Qmin
Qmin is the maximum leading MVAr observed at the low side of the generator step up transformer when the unit is operating at its maximum net dependable MW capability. Qmin is calculated from the leading CURL value by adding any auxiliary MVAr loads and any Load Host MVAr (Self Serve) load served from the low side of the generator step up transformer.
Example:
Leading CURL value is -55 MVAr
Auxiliary Load is 5 MVAr
Qmin is -55 – 5 = -60 MVAr
1.4.1.1 Self-Serve Generation
Self-serve generators serve local load that does not flow through the ERCOT transmission system. Generation data should be submitted for self-serve facilities serving self-serve load modeled in the base case. Total self serve generation MWs shall match total self-serve load MWs.
· Any generating unit or plant with gross real power output of at least 50 MW.
· Any self-serve loads with a contract of at least 50 MW of backup power.
1.4.1.2 Coordination with Power Generating Companies
ERCOT shall request Power Generating Companies to provide the following information, in electronic format:
· Data forms from the ERCOT Generation Interconnection Procedure. See Appendix F.
· One-line electrical system drawing of the generator’s network and tie to TSP (or equivalent) in readable electronic format (AutoCAD compatible)